Abstract

Purple senggani (Melastoma malabathricum) is a tropical flowering plant valued for its antioxidant-rich phenolic compounds. Postharvest thermal pretreatments such as water blanching may inactivate enzymes but also affect phenolic stability. This study aimed to evaluate the effects of water blanching at (70, 80, and 90 °C) for 30–180 s on enzymatic activity and phenolic retention in purple senggani flowers. Polyphenol oxidase (PPO) and peroxidase (POD) activities were assessed spectrophotometrically. Ultrasound-assisted extraction followed by high-performance liquid chromatography coupled with a diode array detector analysis was used to identify and quantify key flavonoids. Total phenolic content (TPC) and total antioxidant capacity (TAC) were also measured. The results showed that PPO and POD activities decreased significantly with increasing blanching intensity, with maximum inactivation of 93% and 75%, respectively. However, blanching also led to substantial degradation of flavonoids such as rutin, quercetin 3-glucoside, trifolin, and astragalin, with several compounds falling below detection levels. These reductions were reflected in sharp declines in TPC and TAC values. The study highlights a trade-off between enzyme inactivation and phytochemical preservation. Further comparative studies are needed to identify optimal processing conditions that maintain both enzyme control and antioxidant integrity in phenolic-rich plant materials.

Key words: Enzyme inactivation, flavonoids, HPLC-DAD analysis, polyphenol oxidase, thermal degradation, ultrasound-assisted extraction.